1. Field of the Invention
The present invention relates to improvements in an opposed piston type disc brake used for braking a vehicle.
2. Description of the Related Art
In order to brake a vehicle, disc brakes are commonly used. In the case of conducting braking operation by the disc brake, a pair of pads between which a rotor rotating together with a wheel is interposed are pushed against both sides of the rotor. As the disc brake described above, a floating caliper type disc brake has been conventionally used, in which a caliper having a piston is supported under the condition that the caliper can be freely displaced relative to a support member, which is fixed to a stationary portion of a vehicle, for supporting the pair of pads under the condition that the support member can be freely displaced. In the case of the above floating caliper type disc brake, the piston is arranged only on one side of the rotor, that is, the piston is arranged only on the inner face side of the rotor which becomes the central side in the width direction when the disc brake is assembled to a vehicle.
Recently, opposed piston type disc brakes have come into common use for vehicles of high performance because they can produce an excellent braking force. In the opposed piston type disc brake, there are provided pistons on both sides of a rotor. In the case of braking operation, a pair of pads are pushed against both side faces of the rotor by both the pistons. In this opposed piston type disc brake, the rotor is interposed between the cylinders, and the opening sections of the cylinders are opposed to each other. Since the opposed piston type disc brake is composed in the manner described above, while consideration is given to machining the cylinders, for example, as described in JP-A-8-277858, the body having a plurality of cylinders is divided into an inner body having an attaching portion to be attached to a stationary portion of a vehicle and also having a cylinder on the inner face side, and an outer body having a cylinder on the outer face side. After both the bodies have been machined to form the cylinders in them, they are connected and fixed to each other by bolts.
In the above conventional structure, the bolts for connecting and fixing the inner body and the outer body to each other receive brake torque which is given by the outer pad to the outer body according to the friction caused between the outer side face of the rotor and the outer pad in the process of braking operation. It is necessary for the bolts to withstand this brake torque. Therefore, the diameters of the bolts must be large, and it causes increases in the size and weight. The weight of the disc brake, which is supported at an end portion of the stationary portion of a vehicle, becomes an unsprung weight. Accordingly, even when the weight of the disc brake is increased a little, the running performance of a vehicle is affected by the increased unsprung weight. For the above reasons, it is desired to improve the circumstances.
On the other hand, in JP-A-1-210628, there is disclosed a structure in which bodies having a plurality of cylinders are integrated into one body. However, the structure described in the above patent publication is disadvantageous in that it takes time and labor to machine the cylinders and assemble the opposed piston type disc brake. Therefore, it is impossible to avoid an increase in the manufacturing cost.